Circuit substrate assemblies are widely used, for example, in power electronics modules (PEMs). Power electronics modules are semiconductor modules used in power electronics circuitry. Power electronics modules are employed typically in vehicular, rail and industrial applications, for example in inverters or rectifiers. They likewise find application in the form of energy generation and transmission. The semiconductor components contained in the power electronics modules may involve e.g. semiconductor chips including an insulated gate (IGBT) or metal oxide field-effect transistor (MOSFET). These IGBT and MOSFET semiconductor chips vary as to their voltage and current handling capacity. Some power electronics modules also comprise in the semiconductor assembly additional semiconductor diodes (i.e. flywheel diodes) for overvoltage protection. Such semiconductor chips may likewise comprise thyristors, diodes or any other power components.
For mounting and circuiting semiconductor chips flat ceramic-based insulating substrates are employed metallized on one or both sides. As compared to mounting the semiconductor chip on a mainly metallic circuit substrate a few millimeters thick, mounting it on such an insulating substrate has the advantage of achieving a relatively good stability to changing temperatures since the thermal coefficient of expansion of a ceramic differs less from the thermal coefficient of expansion of a semiconductor chip (approx. 2 ppm) than that of metal. A further advantage involves the dielectric strength of the ceramic coupled with good thermal conductivity.
However, the thermal conductivity of ceramics is less than that of metals. This is why relatively thin ceramic-based insulating substrates are strived for, but the mechanical bending load capacity of which is low. Such ceramic-based insulating substrates are thus often mounted on rugged baseplates, for example, copper or aluminum based metal plates.
One aspect of the present invention is to provide a method for fabricating a circuit substrate assembly comprising a metallic baseplate bonded to a ceramic substrate stable to changing temperatures. A further aspect is to provide a method for fabricating a power semiconductor module including such a circuit substrate assembly.